Unlike the extra corporeal system used in hemodialysis (HD) to treat end stage renal disease (ESRD), PD makes use of the internal peritoneal membrane to purify the blood of ESRD patients. The two modalities for carrying out PD are automated peritoneal dialysis (APD) and the manual non-automated procedure of continuous ambulatory peritoneal dialysis (CAPD). According to the latter method, dialysis fluid is exchanged from four to six times throughout the day, every day. The fluid remains inside the patient for about four hours between exchanges and for a much longer period (10-12 hours) at night.
It has become conventional to refer to the basic stages of the PD procedure as FILL, DWELL and DRAIN. In the FILL, stage, dialysate is instilled through a catheter into the peritoneal cavity of a patient.
During the fixed time period known as the DWELL, the dialysate draws soluble waste and excess fluid from blood contained in numerous blood vessels of the peritoneal membrane, by the operation of osmosis and diffusion. Additionally, the dialysate re-balances the electrolyte concentration and corrects for acidosis of the blood.
At the end of the DWELL, spent dialysate is removed from the peritoneal cavity (DRAIN) and discarded. This exchange action must be repeated several times over a twenty-four hour period, as the body continuously produces waste products.
Compared with HD, PD is a very gentle modality, its slow corrective action resembling that of the natural kidney. It is operationally simple, eliminates the need for venipunctures and has low operational costs. Because the system is not an extracorporeal one, there is no need for a high degree of heparinization, a factor which is especially important in the case of diabetic patients.
However, to date HD has continued to dominate in the treatment of ESRD patients. The following aspects of PD may be contributing factors to this state of affairs:
In PD, the peritoneal membrane is exposed to the external environment every time a catheter is connected or disconnected from the solution supply, making infection (peritonitis) a significant problem. PA1 Currently available commercial dialysate for PD exhibits a low pH which is not truly compatible with the biochemistry of the peritoneal membrane. Consequently this bio-incompatibility is believed to be one of the factors which eventually degrades the performance of the membrane with time. PA1 The most popular osmotic agent used in PD dialysates is glucose. Glucose can be absorbed by the body via the peritoneum membrane. This can result in patient obesity and its accompanying complications. Moreover, heat sterilization of the dialysate which contains glucose produces harmful glucose by-products. PA1 Current techniques of PD afford no ability to monitor the pressure build-up in the peritoneum during either DWELL or during the FILL sequence. PA1 Current PD solutions are of fixed composition and cannot be systematically adjusted either in their constituent parts or in the concentration of each constituent during a treatment. PA1 (i) Continuous Cycling Peritoneal Dialysis (CCPD), a method of performing PD in which an automated cycler performs 4 to 6 regular exchanges every night. PA1 (ii) Intermittent Peritoneal Dialysis (IPD), a method of performing PD in hospitals or at home with an automatic cycler two or three times a week for a period of about eight to twenty hours each time. PA1 (iii) Nightly Peritoneal Dialysis (NPD), a method of performing nightly peritoneal dialysis at home for patients with high efficiency peritoneal membranes. Such patients do not fare well with long dialysate DWELL times. PA1 (iv) Tidal Peritoneal Dialysis (TPD). This modality utilizes an initial maximum dialysate fill volume (usually three litres) and periodically, during a long and continuous DWELL time, drains a fraction of the fill volume (usually one third, the tidal volume) and re-infuses about a similar amount, adjusting for ultrafiltration (excess fluid removed from the patient's body during kidney dialysis) into the patient. PA1 (i) The low pH of the current commercially available dialysate that is not bio-compatible with the peritoneal membrane (reduces the efficiency of the membrane with time). PA1 (ii) Excessive glucose absorption by the patient (glucose is the most popular osmotic agent). PA1 (iii) Harmful by-products of glucose produced during heat sterilization of the dialysate (adverse to the peritoneal membrane and therefore shortens PD lifetime). PA1 (iv) Excessive pressure build-up in the peritoneum during DWELL period (damage to the peritoneal membrane--hernias and leaks). PA1 (v) Inability to monitor the ultrafiltration (UF) rates on-line to determine the effects of medications on the solute transport (vessel dilators or constrictors leading to higher or lower membrane transports respectively), and profoundly affecting adequacy of treatment. PA1 (vi) Lack of any provision for regulating osmotic concentrations or alternating different osmotic agents during treatment (to optimize solute removal). PA1 (vii) Lack of accessories to automatically add accurate dosage of medication on-line to patient during treatment (advantage to children, to diabetics, to geriatrics and, reduction of contamination). PA1 (i) the rates of infusion of fluid into the patient, PA1 (ii) the removal of fluid from the patient, and PA1 (iii) the customised composition of the dialysate, thereby to allow for control of the patient's intraperitoneal pressure, measurement of peritoneal rates of ultrafiltration and other properties of the peritoneal membrane.
A number of examples of more or less automated peritoneal dialysis machines are to be found in the art, which may be classified into "continuous cycle" PD systems and "batch" PD systems.
In continuous cycle systems, exemplified by U.S. Pat. Nos. 5,004,459 (Peabody et al.) and 5,643,201 (Peabody et al.), the aforementioned DWELL time is essentially zero. Dialysate is delivered by injection into the peritoneal cavity of a patient, simultaneously with the removal of fluid, in a flow-through process.
Continuous cycle processing employs a great amount of dialysis fluid, making it prohibitively expensive for chronic treatment. Known continuous cycle PD systems rely upon the on-site generation of dialysis fluids employing a reverse osmosis water purification unit (connected to an outside water source), and a dialysate proportioning unit, each such unit being about the size of a normal portable household refrigerator. The apparatus is relatively complex, the fluid proportioning itself often comprising more than two independent pumps with fixed proportioning ratios. This leads to difficulties in operation which are complicated by the need for sterilization procedures and pre- and post-sterilization safety tests.
Applications of continuous flow PD systems are limited to treatment of chronic patients, two or three times per week, with the assistance of a competent helper. The intermittent treatment schedule does not provide adequate PD treatment for a number of chronic patients, particularly those exhibiting little or no residual kidney functions. Hence, this type of PD system has fallen almost entirely into disuse.
Known systems for carrying out batch processing, in which there is an appreciable DWELL time during which the effective dialysis step occurs, are exemplified by U.S. Pat. No. 4,096,859 (Agarwal et al.); U.S. Pat. No. 5,141,492 (Dadson et al.); U.S. Pat. No. 5,324,422 (Colleran et al.); and U.S. Pat. No. 5,348,510 (Bryant et al.).
In a continuing effort to provide adequate PD treatment for the varied population of ESRD patients, clinicians have developed a number of different forms of the APD modality of treatment using batch-type PD systems. These include the APD modalities of:
However, even the existing batch-type systems have not proven to be entirely satisfactory in addressing real clinical concerns and implementing the above-listed PD modalities effectively. Some of the major limitations presented by existing systems are:
General Description of the Invention
Applicant's overall objective was to provide an automated peritoneal dialysis machine capable of fully "customizing" the composition of dialysate delivered to a patient to meet his or her immediate physiological needs and, to that same end, capable of monitoring the effectiveness of treatment during the treatment process and use this diagnostic information to optimise the customisation process.
It is a particular object of the invention to provide an automated peritoneal dialysis apparatus as aforesaid, including means for metering solutions of osmotic agent, electrolytes and other desired dialysale components from separate solution containers into mixing chamber means for combination, in desired proportions, to provide the desired dialysis fluid and for delivering a selected quantity of said dialysis fluid to the peritoneal cavity of a patient.
It is likewise an object of the present invention to provide automated peritoneal dialysis apparatus as aforesaid, wherein said means for metering dialysate components into the mixing chamber and delivering dialysis fluid to the patient includes means for withdrawing spent dialysis fluid from the patient. According to a preferred embodiment of the invention, a single pump metering means is provided which is capable of performing multiple functions of metering, infusion, proportioning and removal of the dialysis fluid.
It is a still further object of the invention to provide automated peritoneal dialysis apparatus as aforesaid, wherein the means for delivery of fresh dialysis fluid to a patient and for removing spent dialysis fluid from the patient includes means for monitoring interperitoneal pressure and electronic control means responsive to the signal of said pressure monitoring means, for controlling
It is a further object of the invention to provide automated peritoneal dialysis as aforesaid, in which the manifold, occlusion means and syringe pump means are housed within a compact integral cartridge. Advantageously, the cartridge is furnished with presterilized container bags of dialysate solution in operative connection to the manifold, as a ready-to-use assembly.